Rotating bands for projectiles and methods for making the same



nited States ROTATING BANDS FOR PROJECTILES AND lVIETI-IODS FOR MAKING THE SAME The present invention relates to rotating bands for projectiles.

Up to this time, said bands have been generally made of copper. This metal has physical characteristics which comply particularly well with the requirements for rotating bands. However, copper is a relatively rare and expensive metal and it is desirable to be able to replace it by other materials. This is why rotating bands for projectiles have been made of soft iron and in particular sintered iron and such rotating bands have proved to be satisfactory for an average and high shell velocities and firing rates.

For higher shell velocities and firing rates, as are required at the present time, soft iron and sintered iron rotating bands have shown some drawbacks and in particular a tendency to weld with the steel of the gun barrel and to seize in said barrel. Furthermore in the case of iron powder compressed to ahigh density, wear and tear of the barrel are too great.

The object of my invention is to provide a rotating band for projectiles which is free from these drawbacks. For this purpose, the rotating band according to my inven tion is essentially constituted by a soft nitrided iron powder sintered to the designed shape. In order to reduce the very high temperature which is applied for sintering iron powders to a value admissible for a soft nitrogen treated iron powder, I add to said powder from 0.8 to 2.0% by weight of copper to the iron powder. In order to achieve a uniform distribution of copper in the iron powder, this copper is added by subjecting the iron powder to a chemical copper depositing treatment.

Searches concerning nitrided irons and steels have I shown that the resistance of nitrided surfaces to wear and tear does not depend essentially upon the superficial hardness which can be obtained by nitriding. Practically pure iron samples were subjected to a treatment by ammonia gas or nitriding salt baths at a temperature ranging from 300 to 400 C. It was found that the surfaces of samples thus treated had undergone practically no hardening in the course of this treatment. Therefore this process was called soft nitriding in opposition to the conventional process of nitriding alloy steels which hardens the surfaces of the treated articles. Soft nitrided iron is characterized by its high resistance to wear and tear and by the fact that it has no tendency to seize or to weld with other iron bodies.

2,979,810 Patented Apr. 18, 1961 The rotating bands for projectiles obtained, according to the invention, by sintering of soft nitrided iron powders differentiate from ordinary metallic bodies which have undergone a soft nitriding treatment because said sintered bands have properties uniform throughout their mass Whereas ordinary nitrided metallic bodies are only nitrided in their superficial layer. I will now give an example of my method of manufacturing rotating bands.

Example An iron powder suitable for sintering and having for instance a grain size ranging from 0.1 to 0.15 mm. in diameter is treated in a stream of ammonia gas at a temperature ranging from 300 to 400 C. Advantageously the powder undergoing this treatment is stirred by the gaseous stream which forms eddies in the treatment chamber and if the treatment is performed in this way, it may be completed in about fifteen minutes.

After cooling in a protective gas such as nitrogen, the iron powder thus treated is chemically coated with copper. For this purpose, I may advantageously use a bath consisting in:

500 gr. of distilled water 17 gr. of copper sulfate 1 gr. of tartaric acid 3.5 cm. of 30% ammonia This bath is mechanically stirred and during this operation 250 gr, of iron powder treated as above stated are added thereinto. The copper depositing reaches its optimum value in three minutes. This bath can easily be determined in such manner that the copper deposit on the iron powder grains does not exceed the desired amount. The iron powder obtained after this operation forms the material which is sintered to form the rotating bands. The compression applied for sintering ranges from 3 to 4 metric tons per square centimeter. The sintering operation is conducted at a temperature ranging from 820 to 900 C. for a time ranging from 1 to 2 hours in a reducing gas preferably constituted by hydrogen.

Rotating bands obtained as above stated can be machined without difficulties if it is found necessary.

What I claim is:

1. A process of making a rotating band for a projectile comprising forming a mass of substantially pure iron powder of suitable character for sintering, contacting the mass of powder with gaseous ammonia at a temperature of about 300400 C, to soft nitride the powder, and compacting and sintering the soft nitrided iron powder to the shape of said rotating band.

2. A rotating band for a projectile made by the process of claim 1.

References Cited in the file of this patent UNITED STATES PATENTS 2,323,162 Talmadge Jan. 29, 1943 2,411,073 Whitney Nov. 12, 1946 2,483,075 Truesdale Sept. 27, 1949 2,666,724 Beller Jan, 19, 1954 2,812,276 West Nov. 5, 1957 

